Stress and Sleep Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Stress and Sleep Study (NCT05218109), a randomized na study. The primary outcome is Acceptability of the Combined tVNS + Mindfulness Intervention as Assessed by Participant Self-report of Acceptability Using the Acceptability of Intervention Measure (AIM).

2. Clinical Question

The primary question is whether participants who received transcutaneous vagus nerve stimulation (tVNS) alongside mindfulness rated the combined intervention as acceptable at Week 2, and how those ratings compared with ratings from participants receiving sham tVNS alongside mindfulness. The endpoint was participant self-report on the Acceptability of Intervention Measure (AIM), a four-item questionnaire scored from 1 to 5, with higher scores indicating greater acceptability.

The study also included a mindfulness-only group and a control group assigned a number puzzle task delivered through a mobile device. Primary endpoint results are not reported for those two groups in the registry record. The record describes the study as a longitudinal pilot intended to explore acceptability and preliminary outcomes, but the posted primary result concerns the acceptability measure only. Accordingly, the reported contrast is a focused comparison of two groups sharing the mindfulness component, with active versus sham stimulation.

3. Trial Design

This was a randomized, single-masked, parallel-group pilot study. The registry record lists an enrollment of 76 and describes the participants as healthy college students. The study status is completed. Randomization means participants were assigned to study groups by chance, but the method used to generate or conceal assignments is not reported in the registry record. The identity of the party or parties masked is also not reported, so the meaning of single masking cannot be specified further.

Four groups are described: tVNS plus mindfulness, sham tVNS plus mindfulness, mindfulness only, and control. The control activity was a number puzzle task delivered via mobile device. The registry identifies tVNS and sham tVNS as device interventions and mindfulness as a behavioral intervention. Details of the mindfulness-only arm are not reported in its arm description. The primary comparison uses only the tVNS plus mindfulness and sham plus mindfulness groups, which helps isolate the contrast associated with active versus sham stimulation in the context of mindfulness. It is not a comparison of the combined intervention with no intervention.

The primary endpoint was assessed at Week 2 in the two groups included in the primary comparison. The results population was participants in those groups who completed the Week 2 questionnaires at the appropriate timeframe. The reported analysis includes 12 participants in the tVNS plus mindfulness group and 14 in the sham plus mindfulness group. These endpoint counts are not the same as the listed enrollment, and the registry record does not provide a complete account of the difference between enrollment and the endpoint analysis population.

The study ran from 2022-02-09 to primary completion on 2023-04-28. The registry describes its aim as exploring acceptability and preliminary outcomes related to stress and sleep. The original sample-size assumptions, detailed allocation procedures, intervention schedules, and full statistical analysis plan are not reported in the registry record. The posted primary result is an acceptability score; results for stress and sleep outcomes are not included among the posted secondary results.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Participants were assigned to study arms/groups pseudo-randomly upon scheduling an intake appointment (prior to enrollment).

Overall Study

Analysis population for the primary outcome, as defined in the registry: Enrolled participants in the tVNS + mindfulness groups and sham + mindfulness groups who completed the Week 2 questionnaires at the appropriate timeframe were included in the analysis. Results are not reported for the Mindfulness only and Control groups, as these participants did not receive the tVNS portion of the combined intervention. Therefore, they did not complete the AIM measure asking about acceptability of the tVNS intervention and data was not available to report on for those groups.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: 1 participant in the tVNS + mindfulness group and 3 participants in the sham + mindfulness group were screened out of the study during the intake visit after enrollment.

6. Primary Endpoint

The registry lists the primary outcome as Acceptability of the Combined tVNS + Mindfulness Intervention as Assessed by Participant Self-report of Acceptability Using the Acceptability of Intervention Measure (AIM), measured over Assessed in the tVNS + mindfulness groups and sham + mindfulness groups at Week 2.

The primary endpoint is the mean score on the Acceptability of Intervention Measure (AIM) at Week 2. The registry describes the AIM as a brief four-item scale measuring how acceptable participants believe an intervention to be. Each item is rated from 1, completely disagree, to 5, completely agree. The four item responses are averaged to produce a total score from 1 to 5; higher scores indicate greater reported acceptability.

Acceptability is useful in a pilot study because participants’ views can indicate whether an intervention is regarded as acceptable by those who experienced it. It is distinct from effectiveness, adherence, feasibility, and clinical outcomes: a rating of acceptability does not itself establish whether stress or sleep changed, whether participants completed the intervention as intended, or whether the intervention would be suitable in other settings. The registry record names the measure and its scoring direction, but does not report evidence about the scale’s performance in this particular study.

The endpoint was assessed in the tVNS plus mindfulness and sham plus mindfulness groups at Week 2. The registry states that participants in the mindfulness-only and control groups did not receive tVNS and that results are not reported for those groups. Thus, the primary endpoint result addresses participant ratings for the two groups that combined mindfulness with active or sham stimulation. It does not provide a complete acceptability comparison across all four study groups.

7. Results Posted in the Registry

• tVNS + Mindfulness: mean 4.08 versus 3.37 on control; difference 0.71 (95% CI 0.07 to 1.35), standardized effect d = 0.80; z-test p = 0.031.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: each participant’s AIM total is a numerical score, and the registry reports a mean and standard deviation for each group. The comparison is therefore expressed as a difference between group means. The posted estimate is 0.71 units, calculated as the tVNS plus mindfulness mean relative to the sham plus mindfulness mean. A positive difference indicates a higher average AIM score in the tVNS plus mindfulness group, consistent with the scale’s direction, where higher scores indicate greater acceptability.

What does the mean describe?

A mean is the arithmetic average of participants’ scores in a group. It provides a compact description of the group’s central score, but does not show every individual response or the shape of the score distribution. The registry reports means of 4.08 and 3.37. The standard deviations are 0.4 and 1.15, respectively. A standard deviation describes how dispersed observations are around their group mean: a larger value indicates greater spread among the observed scores. These summaries do not reveal whether scores were symmetric, clustered at particular response values, or affected by extreme observations.

How should the group difference be read?

The mean difference compares the two group averages in the endpoint analysis. It is an unadjusted contrast in the posted summary, rather than an estimate explicitly adjusted for baseline measurements or other characteristics. The registry gives an interval around the difference and an unadjusted p-value of 0.031. The exact statistical model, interval confidence level, and detailed calculation procedure are not reported in the registry record. Therefore, the result can be described using the posted estimate and uncertainty interval, but the underlying analytic assumptions cannot be independently characterized from the record.

General statistical explanation: an interval estimate reflects uncertainty about the population contrast that could have generated the observed group data, conditional on the method and assumptions used. It is not a range containing a known proportion of individual participant scores. The interval in this record is positive at its lower endpoint, which is close to zero, and reaches 1.354 at its upper endpoint. Because the confidence level is not identified in the registry record, it should not be labelled with a particular confidence percentage.

What does the p-value add?

General statistical explanation: a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the analysis assumptions were true. It is not the probability that the null hypothesis is true, nor is it a measure of the size or practical importance of a difference. The reported p-value is unadjusted. It does not on its own account for the possibility of examining multiple outcomes, groups, or comparisons, and the record does not specify a multiplicity strategy.

Randomized assignment can support a causal comparison when the study is conducted and analyzed as planned, but the registry record does not provide enough detail to assess all relevant design and analysis features. In particular, it does not report the randomization procedure, allocation concealment, the identity of the masked party, or the complete statistical plan. The analysis population is described as participants in the two groups who completed the Week 2 questionnaires at the appropriate timeframe. This is not enough to establish whether the analysis followed an intention-to-treat principle or how missing endpoint data were handled.

Why does dispersion matter?

General statistical explanation: variability affects how precisely a group mean and a between-group contrast can be estimated. When responses vary widely among participants, a given group size usually provides less precise information about the average than when responses are more tightly clustered. The reported standard deviation is greater in the sham plus mindfulness group than in the tVNS plus mindfulness group, and the group sizes are limited. The interval around the difference reflects uncertainty, although its exact construction is not stated.

General statistical explanation: over-dispersion refers to variability greater than a statistical model expects. If present, it can make standard errors too small and intervals too narrow when the model does not account for the extra variation. The registry record does not report a model diagnostic or identify an over-dispersion issue for this continuous endpoint. It would therefore be inappropriate to claim that over-dispersion occurred or that a particular correction was used. The general point is that variability and model assumptions matter for interpreting precision, especially in a small pilot comparison.

The posted comparison should consequently be read as a summary of observed Week 2 AIM scores with a reported unadjusted difference, interval, and p-value. It is not a complete account of every analytic choice, and the registry record does not report an analysis for the other two groups or results for secondary outcomes.

10. Confidence Intervals and Precision

The reported mean difference is 0.71 AIM units, and the posted interval runs from a positive lower endpoint close to zero to 1.354. This interval communicates uncertainty in the estimated contrast: the observed difference is not known with exact precision, and values spanning a small positive contrast through a larger positive contrast remain compatible with the reported analysis. The interval’s lower endpoint is close enough to zero that the data do not pin down the size of the positive difference precisely.

The confidence level and method used to construct the interval are not reported in the registry record. It is therefore not appropriate to assign it a confidence percentage or to compare it with an interval calculated under a presumed method. The p-value of 0.031 is reported as unadjusted, and does not substitute for reading the interval. The estimate conveys direction and magnitude on the AIM scale; the interval conveys uncertainty around that estimate, while the p-value addresses compatibility with a specified null under statistical assumptions.

Precision is also constrained by the number of endpoint observations: 12 participants in the tVNS plus mindfulness group and 14 in the sham plus mindfulness group. The reported standard deviations differ between groups, with greater observed variation in the sham plus mindfulness group. Both the limited group sizes and the observed spread are relevant when judging how stably the group means and their difference represent a broader population. The registry record does not give a minimal important difference for the AIM, so the interval cannot be classified as spanning or excluding a threshold for meaningful acceptability change.

These are participant-reported acceptability scores from the specified Week 2 comparison. Precision around this contrast should not be extended to stress, sleep, the other study arms, later follow-up, or populations beyond the analyzed participants. The registry record does not report those endpoint estimates in the posted secondary results.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations expressed as participants per arm, not total event counts. The assumptions listed for this illustration are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect. These are planning assumptions for the illustration; the trial’s own original design assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the illustration gives 25 participants per arm for 80% power and 33 participants per arm for 90% power. At 75% of the observed effect, it gives 44 participants per arm for 80% power and 59 participants per arm for 90% power. At 50% of the observed effect, it gives 99 participants per arm for 80% power and 132 participants per arm for 90% power. The curve expresses the same relationship visually: as the effect size being planned for becomes smaller, the required number of participants per arm increases.

In plain language, the 80% power column describes the number of participants per arm the illustration estimates would be needed to have an 80% chance of detecting the specified effect under the stated assumptions. The 90% column uses a higher chance of detection and therefore calls for larger groups. These are hypothetical planning counts based on the observed effect and should not be read as the study’s original target or as a description of the enrollment achieved. This is not observed power.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.710; pooled standard deviation σ = 0.889.
2. n = 2 × (1.96 + 0.842)² × 0.889² / 0.710² = 24.6, rounded up to 25 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 0.71                      # observed difference in means
sigma <- 0.888643629358811                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(5218109)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 25 (80% power), 33 (90% power)
 75% of observed effect: n per arm = 44 (80% power), 59 (90% power)
 50% of observed effect: n per arm = 99 (80% power), 132 (90% power)
power.t.test: 25.6 
Simulated power at n = 25 per arm: 0.792 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists three outcome measures but no posted secondary results. It lists no analyses. The primary result presented is the Week 2 AIM comparison between tVNS plus mindfulness and sham plus mindfulness. No multiplicity adjustment, hierarchy of tests, or prespecified strategy for selecting outcomes is reported in the registry record. Since the reported p-value is unadjusted, it should be interpreted as applying to that contrast without assuming that it accounts for other possible analyses.

General statistical explanation: when multiple hypotheses are tested, the chance of at least one apparently unusual result can increase if no multiplicity strategy is used. A prespecified hierarchy or adjustment can help address this issue, but the record does not say whether either was planned. The absence of posted secondary results also means the primary result cannot be considered alongside a complete set of outcome findings from the study.

The primary endpoint population is described as enrolled participants in the tVNS plus mindfulness and sham plus mindfulness groups who completed the Week 2 questionnaires at the appropriate timeframe. The reported endpoint counts are 12 and 14. The record does not provide a participant flow accounting for all enrolled participants, reasons for non-completion, or the amount and pattern of missing data. It does not report imputation, a missing-data sensitivity analysis, or how incomplete questionnaires were handled.

The analysis population for the other two groups is not reported for this primary endpoint, and no results are posted for them. The record also does not state whether the primary analysis included participants according to their randomized assignment regardless of intervention completion. Therefore, the analysis cannot be identified as intention-to-treat, per-protocol, or another formally defined population from the registry record. These omissions limit assessment of potential bias from missing outcomes, exclusions, and analytic choices. They do not demonstrate that any particular problem occurred; they mean the relevant details are not reported in the registry record.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports no serious adverse events in any of the four groups. The serious-event risk sets are 16 participants for tVNS plus mindfulness, 20 for sham plus mindfulness, 20 for mindfulness only, and 20 for control; the serious-event count is 0 in each group. Deaths are also reported as 0 in each group. These figures describe the serious-event counts recorded for the listed risk sets and do not establish that no unrecorded events occurred.

Serious adverse events are a distinct category from other adverse events. The record lists 3 other adverse events in the sham plus mindfulness group and 0 in the other groups. No serious adverse event terms are listed. The registry record does not provide additional event descriptions or enough detail to assess event timing, relatedness, severity criteria, or follow-up completeness. The risk-set counts differ from the primary endpoint analysis counts; they concern the adverse-event reporting and should not be substituted for the Week 2 AIM sample sizes.

These safety counts are descriptive registry entries. They do not, by themselves, establish comparative safety, particularly because the study is a pilot and group sizes are limited. They should not be interpreted as a prediction of risk outside the participants and observation represented in the record.

15. What the Result Does, and Does Not, Mean

The central statistical finding is a higher average Week 2 acceptability score in the tVNS plus mindfulness group than in the sham plus mindfulness group among participants included in the primary endpoint analysis. The estimated mean difference was 0.71 AIM units. The reported interval indicates uncertainty, with a lower endpoint close to zero and an upper endpoint of 1.354. The unadjusted p-value was 0.031. Together, these quantities describe a positive observed contrast while leaving uncertainty about its precise size.

The result is about acceptability as measured by participant self-report. It does not show whether the interventions improved stress or sleep, whether participants adhered to the interventions, or whether any clinical outcome changed. The study’s stated aims include preliminary outcomes related to stress and sleep, but no secondary results are posted in the registry record. The primary endpoint is not itself a measure of stress or sleep.

The comparison is also limited to two of the four groups: tVNS plus mindfulness and sham plus mindfulness. It cannot be treated as a comparison with mindfulness alone or with the number puzzle control, because primary results for those groups are not reported. The analysis used participants with Week 2 questionnaire data at the appropriate timeframe, rather than all listed enrollment, and the registry does not explain all exclusions or missing observations.

Finally, the statistical record does not report the interval’s confidence level, the full analysis plan, or a threshold for a meaningful difference on the AIM. The mean difference and p-value should therefore not be used alone to claim that the observed contrast is important to participants or that it will recur in another sample. The posted result is a preliminary description of acceptability ratings in this pilot comparison, with uncertainty and reporting limitations that matter when interpreting its scope.

16. Why This Trial Matters Statistically

This study raises a useful statistical distinction between feasibility-oriented outcomes and clinical outcomes. Acceptability is a participant-reported measure, and its mean can be compared between randomized groups, but it answers a different question from whether stress or sleep changed. Keeping the endpoint’s meaning clear prevents a statistically described contrast from being mistaken for evidence about an outcome it does not measure.

The randomized parallel design allows an active-versus-sham comparison while both groups receive mindfulness. That design makes the primary contrast narrower than a comparison of a combined program with no intervention: it focuses on the difference between the two stimulation conditions in the context of mindfulness. At the same time, only two of the four groups contribute to the posted primary result. The reported finding therefore has a defined comparison and should not be generalized to all arms.

The small endpoint groups and the uncertainty interval also illustrate why an estimate and its precision matter together. The mean difference communicates the direction and scale of the observed contrast; the interval shows that its exact size is not firmly determined. A p-value alone would not convey that range of plausible values or indicate whether the contrast is important in practical terms. The registry does not report a meaningful-difference threshold for the AIM.

Finally, the record’s limited detail on missing data, analysis populations, multiplicity, and statistical procedures illustrates how registry reporting affects interpretation. The posted statistics can be described accurately, while several questions about robustness and the completeness of the analysis remain unresolved. Those distinctions are particularly important for a pilot whose stated purpose includes preliminary exploration.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary comparison includes only participants who completed the Week 2 questionnaires at the appropriate timeframe, with 12 participants in the tVNS plus mindfulness group and 14 in the sham plus mindfulness group. The registry record does not report a complete participant flow, reasons for missing questionnaires, or the handling of incomplete items. This limits assessment of whether the analyzed participants differ from those not included.

Results are not reported for the mindfulness-only and control groups, so the primary outcome cannot describe acceptability across all four arms. No secondary results are posted, despite the study’s stated interest in preliminary outcomes related to stress and sleep. The record lists three outcome measures but does not provide their additional results. This leaves the overall outcome picture incomplete.

Several design and analysis details are not reported in the registry record, including the randomization procedure, the identity of the masked party, the original sample-size assumptions, the full statistical analysis plan, and the method used to construct the interval. The interval confidence level is not stated. The record also does not describe multiplicity handling, missing-data methods, or whether the analysis followed randomized assignment regardless of completion.

The study is described as a pilot, and the endpoint groups are small. The reported standard deviations differ between groups, and the interval for the mean difference extends from near zero to a larger positive value. No threshold for a meaningful AIM difference is reported. Consequently, the estimate’s practical importance and stability are difficult to judge from this result alone. These reporting limits do not establish that the analyses were inadequate; they identify details that are not reported in the registry record.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Stress and Sleep Study — NCT05218109.
• Registry record last updated 2024-04-04; status last verified 2024-04.
• Results first posted 2024-04-04.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

NCT05218109, titled Stress and Sleep Study, is a completed randomized, single-masked, parallel-group pilot study sponsored by the University of Florida. It enrolled 76 healthy college students and included tVNS plus mindfulness, sham plus mindfulness, mindfulness only, and control groups. The primary endpoint was Week 2 acceptability measured by the AIM in the two groups receiving stimulation with mindfulness.

The reported mean AIM scores were 4.08 for tVNS plus mindfulness and 3.37 for sham plus mindfulness, with a mean difference of 0.71 units, a reported interval extending from just above zero to 1.354, and an unadjusted p-value of 0.031. Primary results are not reported for the mindfulness-only and control groups, and no secondary results are posted. The registry record does not report the full statistical plan, interval confidence level, or detailed missing-data procedures.